This invention relates to circuit components mounted on circuit boards by solder column interconnects or arrays, and more particularly, to column grid arrays and supporting them.
Solder column interconnects or arrays are used to interconnect circuit packages to circuit boards, most typically large ceramic integrated circuit packages. One such package is the column grid array package that has a ceramic substrate with a series of solder columns that extend out from it, typically from the bottom surface. The solder columns are attached at one end to connection pads or locations on the ceramic substrate. The solder columns are sufficiently tall so that when the circuit package is placed on a circuit board, the solder columns can accommodate the difference in thermal expansion between the ceramic integrated circuit package and the printed circuit board. The solder columns are soldered to respective pads on the circuit board using known techniques, such as a convection reflow solder process.
One problem with solder column arrays is that the solder columns do not withstand compressive force well. The solder columns in the solder column arrays are typically made of a 90%/10% Pb/Sn solder, which is a soft material. Moreover, the individual solder columns are very thin. Consequently, if any significant amount of compressive force is applied to the circuit package, such as might be applied by a cooling solution such as a heat sink or fan, the resulting weight on the circuit package may cause the solder column array to compress, particularly over time, which may compromise reliability. In this regard, loads in excess of about 10 to 20 grams per column exert sufficient compressive force so that reliability may be compromised. Since CGA integrated circuit packages are being increasingly used for high power integrated circuits, the cooling solution required often has considerable mass. It is not unusual for the heat sink or cooling solution used with such high power integrated circuits to exceed one pound.
In accordance with the invention, a circuit package has connection locations or pads, some of which must be electrically connected to pads on a circuit board to which the circuit package is mounted and others of which do not. A solder column array has solder columns connected to the pads of the circuit package. In at least one of the no-connect locations, that is, the connection locations or pads of the circuit package that do not need to be electrically connected to a pad on the circuit board, a rigid column is affixed to the connection pad in lieu of a solder column. In an aspect of the invention, a plurality of rigid columns are interspersed throughout the solder column array in at least some of the no-connect locations. The rigid column or columns extend between the circuit package and the circuit board and support the circuit package against compressive force. In an aspect of the invention, the rigid columns are attached to respective connection pads of the circuit package at the no-connect locations but not soldered to respective connection pads on the circuit board.
In an aspect of the invention, the circuit package is a column grid array having a two dimensional solder column array having a plurality of solder columns with rigid columns interspersed therewith, the rigid columns being in no-connect locations.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.